The use of touch screen displays as input devices for computers and other electronic devices has increased significantly in recent years. Some touch screen displays permit direct finger manipulation of on-screen objects in a manner that resembles manipulation of physical objects in the physical world, rather than requiring indirect manipulation of on-screen objects (e.g., via a cursor). In general, touch screen interfaces that closely emulate the physical world provide a more transparent and intuitive experience to a user because the user can simply use the touch screen interface based on their understanding of the physical world.
But existing touch screen interfaces with direct finger manipulation of on-screen objects have limitations in their abilities to emulate interaction with real world objects. For example, touch screen interfaces typically convert a finger contact on the touch screen into a single point (e.g., the centroid of the detected finger contact) and then use this point to interact with objects on the touch screen. If the single point does not overlap with an on-screen object, even though other parts of the finger contact do overlap with the object, then the object may not be selected for manipulation by the user. Thus, more precise positioning of the finger contact is needed to interact with an object, which in turn obscures more of the object during manipulation. In addition, with each finger contact converted to a single point, at least two fingers are required to rotate an object.
Accordingly, there is a need for electronic devices with more transparent and intuitive user interfaces for moving on-screen objects in accordance with finger contacts and movements on a touch screen display without using a cursor to move the objects. Such interfaces increase the effectiveness, efficiency, and user satisfaction with electronic devices with touch screen displays.